|Hjelmfelt Jr, Allen|
Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: 9/20/1995
Publication Date: N/A
Interpretive Summary: Constructed subsurface flow wetlands are gaining increasing acceptance for use in small waste-water treatment systems. The hydraulics of such systems are unusual due to their shallow depth, to use of uniform size rock, and to the plant root system. This paper describes an experimental investigation conducted to quantify the hydraulic parameters needed for design of subsurface flow wetlands. Commonly used design equations were modified to account for the presence of plant roots. Predictions obtained with these modified equations agreed with experimental data more closely than predictors obtained with the unmodified equations.
Technical Abstract: Ergun's equation was modified to account for the additional flow resistance of roots within a constructed rockbed flume. Comparison of head loss for a range of flow rates through two sizes of rock media (creek rock diameter of 1.81 cm and pea gravel diameter of 0.62 cm) indicated that these modifications improved prediction of head loss compared to Ergun's equation nwith no modification. Flow through creek rock with roots was more sensitive to tortuosity and friction coefficients than was pea gravel. Differences in head loss between the two media would be expected to decrease with continued root growth.